Tandem-PHD: Acetylated lysines (AcKs) can be recognized by the tandem PHD domain. Besides, the bromo domain of Brdt has a much wider pocket, which holds two AcKs simultaneously; whereas the tandem PHD has a shallow cage. Many bromo domains bind to multiple acetylated histones and the tandem PHD domain of human DPF3b also prefers acetylated H3 and H4, indicating the lack of unique sequence recognition by these readers. (1)